Pressure gauge with automatically operated pressure relief valve

ABSTRACT

A pressure gauge having a pressure operated piston for measuring the difference in pressure between two pressure signals including an automatically operative pressure relief valve and a manually operable three-way valve to provide a venting function useful for inspecting the operation of the pressure operated piston of the pressure gauge.

This is a continuation of PCT/US00/10296 filed Apr. 17, 2000 and claimspriority of provisional patent application Serial No. 60/130,895, filedApr. 23, 1999.

FIELD OF THE INVENTION

The present invention relates to a pressure gauge and more particularlyto a gauge for measuring the difference in pressure between two pressuresignals and an associated pressure relieving feature.

BACKGROUND OF THE INVENTION

Differential pressure can be determined in many ways. One of thesimplest methods of determining differential pressure is to measure orobserve the motion of a close fitting piston balanced by a spring in acylinder. A higher pressure is applied to the end of the cylinder not incommunication with the spring and a lower pressure is applied to the endof the cylinder in communication with the spring. Accordingly, thehigher pressure will cause the piston to move. The spring will be causedto compress until the force required to compress the spring added to theforce caused by the lower pressure equals the force caused by the higherpressure. The distance that the piston travels can be measured and whencarefully calibrated in terms of pressure differential will provide areading of the difference between the high and low pressures.

Differential pressure gauges of the spring-balanced piston type aresubject to erratic operation due to the disposition and collection ofcontamination in the clearance space between the piston and theassociated cylinder. Typically, the clearance of the piston and thecylinder is very small (approximately 0.0003 inches) so that there isvery little fluid flow possible. No seal is used because it would createfriction thereby decreasing the accuracy of the gauge.

A test for possible contamination in a gauge that has a cylinder made ofglass is commonly performed. The test is typically achieved by closingthe low pressure connection and then venting the cavity beneath thepiston so that the high pressure on top of the piston will drive thepiston over its full length of travel. The operator observes the pistonmotion to detect erratic movement which would be indicative of bindingcaused by contaminating deposits. To provide for this test, it has beencustomary to use a 3-way selector valve located at the port where thelow pressure connection is made.

Another issue which must be considered in the operation of equipmentthat is subject to pressure is to provide for protection againstexcessive pressure by utilizing a pressure relief valve. A commonapplication for a pressure relief valve is on a filter vessel in apipeline system. If the pipeline valves are closed in a way to isolatethe filter vessel, solar heating causes an increase in temperature ofthe fluid in the vessel resulting from thermal expansion of the fluidwhich is far greater than the expansion of the materials used to makethe vessel. The pressure relief valve releases enough fluid to prevent apressure that is greater than the design pressure of the vessel.

If a differential pressure gauge is installed on the vessel, it isprotected from excessive pressure by the pressure relief valve on thevessel. However, if isolation valves are closed which are installed inthe tubing connecting the differential pressure gauge to the vessel, theexcessive pressure in the gauge cannot be relieved. The gauge will breakif the pressure exceeds the design pressure parameters of the gauge. Toavoid this problem, a separate pressure relief valve can be installed onthe gauge at considerable cost.

It is an object of the invention to produce a gauge for measuring apressure differential between two pressure signals including anautomatically operative pressure relief valve.

Another object of the invention is to produce a gauge for measuring apressure differential between two pressure signals including a manuallyoperable spring return push button to provide a venting function usefulfor inspecting the operation of the pressure operated piston of thegauge.

SUMMARY OF THE INVENTION

The above, as well as other objects of the invention, may be readilyachieved by a differential pressure gauge having an automaticallyoperative pressure relief valve and a manually operable three-way valveto provide a venting function useful for inspecting the operation of thepressure operated piston of the pressure gauge.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other objects, features, and advantages of thepresent invention will be understood from the detailed description ofthe preferred embodiments of the present invention with reference to theaccompanying drawings, in which:

FIG. 1 is an elevational view partially in section showing adifferential pressure gauge including a pressure relieving valveincorporating the features of the invention;

FIG. 2 is an enlarged sectional view of the pressure relief valveillustrated in FIG. 1; and

FIG. 3 is a fragmentary sectional view of the pressure relief valveillustrated in FIG. 2 taken along line 3—3 thereof showing the manuallyoperable three-way valve in the depressed position.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring now to the drawings, and particularly FIG. 1, there is showngenerally at 10 a differential pressure gauge incorporating the featuresof the invention. The pressure gauge 10 includes a main housing or cage12.

A translucent glass cylinder 14 is disposed within the cage 12. The endsof the glass cylinder 14 are sealed to an upper flange 16 and a lowerflange 18 with O-rings 20, 22, respectively. The upper flange 16 and thelower flange 18 are removably mounted to the cage 12.

A piston 24 is slidably operable within the glass cylinder 14. Thepiston 24 strictly conforms to the shape of the glass cylinder 14 tomaintain a close tolerance. Typically, the clearance between the outerwall of the piston 24 and the inner wall of the cylinder 14 isapproximately 0.0003 inches or less. The piston 24 is urged by andsupported within the glass cylinder 14 by a helical spring 26. One endof the spring 26 abuts a lip 27 on the flange 18. The opposite end ofthe spring 26 abuts an inner surface of the piston 24.

A nameplate 28 is disposed on the cage 12. A window 30 formed in thenameplate 28 facilitates viewing of the position of the piston 24 withinthe glass cylinder 14. The position of the top of the piston 24 isvisually observed relative to a graduated scale on the nameplate 30 toread the differential pressure.

A high-pressure inlet 32 is in fluid communication with the end of theglass cylinder 14 towards which the piston 24 is being urged by thespring 26. The high-pressure inlet 32 is adapted to be placed in fluidcommunication with a high-pressure source (not shown).

A low-pressure inlet 34 is in fluid communication with the opposite endof the glass cylinder 14 as the high-pressure inlet 32. The low-pressureinlet 34 is adapted to be placed in fluid communication with alow-pressure source (not shown).

Referring now to FIG. 2, there is shown an automatically operatingpressure relief valve. The pressure relief valve is disposed in thepressure gauge 10 adjacent the low pressure inlet 34, as illustrated inFIG. 1. The pressure relief valve includes an inlet port 36. The inletport 36 is in fluid communication with the low-pressure inlet 34.

A hollow fitting 38 is disposed in the flange 18. An O-ring 39 seals theouter surface of the hollow fitting 38 with the flange 18. A valvemember 40 is slidably disposed within the interior portion of the hollowfitting 38. A hole 41 is formed to extend transversely through the valve40. One end of a helical spring 42 abuts the valve 40. The other end ofthe spring 42 abuts an adjusting screw 44. The spring 42 urges the valve40 to seat against an O-ring 46 thereby sealing the valve 40 with thehollow fitting 38.

A clearance or chamber 48 surrounds a portion of the outer wall of thehollow fitting 38 and is in fluid communication with the inlet port 36.A lateral passageway 50 leads from the chamber 48 to a main passageway52. The lateral passageway 50 and the main passageway 52 permit fluidcommunication between the chamber 48 and the glass cylinder 14. Astrainer 54 is disposed in an enlarged portion of the main passageway 52adjacent the glass cylinder 14. A vent port 56 is disposed in the end ofthe hollow fitting 38 to provide fluid communication between the hollowportion of the hollow fitting 38 and a reservoir (not shown) or theatmosphere surrounding the pressure gauge, as desired.

The pressure relief valve structure is combined with additionalstructure to form a manually operable three-way valve to provide aventing function. A hollow insert 58 is disposed in the flange 18opposite the hollow fitting 38. Spaced apart O-rings 60, 62 seal thehollow insert 58 with the flange 18.

A shaft 64 is slidably disposed in the hollow portion of the hollowinsert 58. An O-ring 66 seals the shaft 64 with the hollow insert 58. Achannel 68 is disposed in one end of the shaft 64. A push button 70 isdisposed on the shaft 64 at the opposite end thereof from the channel68. The push button 70 is insertable into an enlarged portion of thehollow insert 58 and extractable therefrom. A depressible normallyoutwardly urged protuberance 72 is disposed in and extends from the pushbutton 70.

In normal operation, the lower pressure fluid reaches the cylindercavity under the piston from low-pressure inlet 34 and passes throughthe inlet port 36 into the chamber 48. The fluid then enters the lateralpassageway 50 and the main passageway 52 before passing through thestrainer 54.

When the push button 70 is pushed inwardly, it is caused to be urgedagainst the end of the valve 40 which, in turn, is restrained by thespring 42, as illustrated in FIG. 3. The adjusting screw 44 can be movedinwardly or outwardly to create the desired restraining force. As theshaft 64 is moved across the inlet port 36, incoming fluid is cut offand continuing motion unseats the O-ring 46 of the valve 40. Theunseating of valve 40 allows the fluid that is under the piston to beforced through the main passageway 52 and the lateral passageway 50 andinto the chamber 48. The fluid can then flow through the hole 41 in thevalve 40 and pass out of the gauge assembly through the vent port 56.The fluid is either discharged through the vent port 56 to theatmosphere or piped away to a reservoir. When the push button 70 isreleased, flow of low-pressure fluid from the low-pressure inlet 34 canthen refill the cavity under the piston.

Under a condition of excessive pressure build-up inside of the gauge,caused by thermal expansion of the liquid, the resulting pressure actson the valve 40 to compress the spring 42 and permit the high pressurefluid to exit through the vent port 56. The depressible protuberance 72prevents the push button 70 from accidentally being depressed.

As described, the valve 40 performs two functions. First, the valveoperates as an automatic pressure relief valve. Second, the valveoperates as a manual 3-way valve that can be activated to perform theventing function that is used to inspect the operation of the piston.Therefore, a benefit of the invention is the replacement of a 3-wayselector valve with a 3-way valve that consists of a spring return pushbutton that performs the same function which also functions as apressure relief valve.

From the foregoing description, one ordinarily skilled in the art caneasily ascertain the essential characteristics of this invention and,without departing from the spirit and scope thereof, can make variouschanges and modifications to the invention to adapt it to various usagesand conditions.

What is claimed is:
 1. A differential pressure gauge for measuring apressure differential between two pressure signals comprising: a mainhousing; a high-pressure inlet in said main housing providing fluidcommunication with a high-pressure source; a low-pressure inlet in saidmain housing providing fluid communication with a low-pressure source; atranslucent hollow cylinder having two ends, the first end of saidcylinder in fluid communication with said high-pressure inlet and thesecond end of said cylinder in fluid communication with saidlow-pressure inlet; a piston slidably disposed within said cylinder; aspring disposed within said cylinder, said spring urging said pistontowards the first end of said cylinder; and a pressure relief valvedisposed in said main housing having a manually operable three-way valveto provide a venting function useful for inspecting the slidingoperation of said piston, wherein said pressure relief valve is in fluidcommunication with said low-pressure inlet and said cylinder.
 2. Thedifferential pressure gauge according to claim 1, including a nameplatehaving a window formed therein, whereby said cylinder is viewablethrough the window.
 3. The differential pressure gauge according toclaim 1, including a push button to operate the three-way valve.
 4. Thedifferential pressure gauge according to claim 1, wherein the clearancebetween said piston and said cylinder is less than 0.0003 inches.
 5. Thedifferential pressure gauge according to claim 1, wherein said pressurerelief valve comprises: a hollow fitting; a valve slidably disposedwithin said hollow fitting; an adjusting screw disposed within saidhollow fitting spaced apart from said valve; a spring disposed betweensaid valve and said adjusting screw, wherein said spring urges saidvalve away from said adjusting screw.
 6. The differential pressure gaugeaccording to claim 5, wherein said adjusting screw is positionable toadjust the force exerted by said spring on said valve.
 7. Thedifferential pressure gauge according to claim 6, wherein said valve hasa hole formed therein.
 8. The differential pressure gauge according toclaim 7, wherein said pressure relief valve further comprises: a hollowinsert disposed adjacent said hollow fitting; a shaft slidably disposedin said hollow insert; and a push button disposed on one end of saidshaft, whereby depressing said push button causes said shaft to contactsaid valve and compress said spring.
 9. The differential pressure gaugeaccording to claim 8, wherein said push button includes a depressibleprotuberance extending therefrom.
 10. A differential pressure gauge formeasuring a pressure differential between two pressure signalscomprising: a main housing; an upper flange disposed on said mainhousing having a high-pressure inlet disposed therein, the high-pressureinlet providing fluid communication with a high-pressure source; a lowerflange disposed on said main housing opposing said upper flange, saidlower flange having a low-pressure inlet disposed therein, thelow-pressure inlet providing fluid communication with a low-pressuresource; a translucent hollow cylinder having two ends, the first end ofsaid cylinder sealed to said upper flange of said main housing and influid communication with the high-pressure inlet, the second end of saidcylinder sealed to said lower flange of said main housing and in fluidcommunication with the low-pressure inlet; a pressure operated pistonslidably disposed within said cylinder; a spring disposed within saidcylinder, said spring urging said piston towards the first end of saidcylinder; and a pressure relief valve disposed in said main housinghaving a manually operable three-way valve to provide a venting functionuseful for inspecting the sliding operation of said pressure operatedpiston, wherein said pressure relief valve is in fluid communicationwith the low-pressure inlet and said cylinder.
 11. The differentialpressure gauge according to claim 10, including a nameplate having awindow formed therein, whereby said cylinder is viewable through thewindow.
 12. The differential pressure gauge according to claim 10,including a push button to operate the three-way valve.
 13. Thedifferential pressure gauge according to claim 10, wherein the clearancebetween said piston and said cylinder is less than 0.0003 inches. 14.The differential pressure gauge according to claim 10, wherein saidpressure relief valve comprises: a hollow fitting; a valve slidablydisposed within said hollow fitting; an adjusting screw disposed withinsaid hollow fitting spaced apart from said valve; a spring disposedbetween said valve and said adjusting screw, wherein said spring urgessaid valve away from said adjusting screw.
 15. The differential pressuregauge according to claim 14, wherein said adjusting screw ispositionable to adjust the force exerted by said spring on said valve.16. The differential pressure gauge according to claim 15, wherein saidvalve has a hole formed therein.
 17. The differential pressure gaugeaccording to claim 16, wherein said pressure relief valve furthercomprises: a hollow insert disposed adjacent said hollow fitting; ashaft slidably disposed in said hollow insert; and a push buttondisposed on one end of said shaft, whereby depressing said push buttoncauses said shaft to contact said valve and compress said spring. 18.The differential pressure gauge according to claim 17, wherein said pushbutton includes a depressible protuberance extending therefrom.